Involvement of Upregulated P53-Induced Death Domain Protein in Retinal Ganglion Cells Apoptosis after Optic Nerve Crush.

Purpose: Retinal ganglion cells (RGCs) apoptosis is a common characteristic of optic neuropathies. p53-induced protein with a death domain (PIDD) is a well-known regulator of genotoxic stress-induced apoptosis, which is constitutively cleaved into three main fragments: PIDD-N, PIDD-C and PIDD-CC. Thus, we aim to determine the physiological relevance of PIDD in RGCs apoptosis in an optic nerve crush (ONC) model. Methods: All animals were evenly randomized into four groups: sham-control group, con-siRNA group, ONC group, and PIDD-siRNA group (ONC +PIDD-siRNA). Expressions of PIDD, caspase-2, Bm3a and tBid in ONC model were analyzed by Western blot and immunofluorescence. Mean densities of RGCs/mm(2) were calculated with Fluoro-Gold (FG). Moreover, we tested the effect of PIDD-siRNA on ONC-induced RGCs apoptosis using TUNEL staining. Results: The level of full-length PIDD was weakly present and showed no significant differences at any time points. PIDD-CC and PIDD-C were significantly up-regulated in the retina at 3 days after ONC. Meanwhile, the expression of PIDD was significantly increased in Brn3a (a marker of RGCs) positive cells, indicating that the localization of PIDD appeared to be confined to RGCs. Furthermore, inhibition of PIDD prevented RGCs apoptosis by inhibiting caspase-2 and tBid activation. Conclusion: Taken together, PIDD may play a crucial role in RGCs apoptosis after ONC, and this process may be relevant to caspase-2 and tBid.